1. Field of the Invention:
The present invention relates to a transmission and, more particularly, a device for controlling an automatic fluid transmission composed of a torque converter and speed change gears for use with automobiles.
2. Description of the Prior Art:
Automatic fluid transmission are generally adapted to make automatic shifting-over among various speed ranges in accordance with a balance in vehicle speed and throttle opening when the speed shift valve is positioned at its automatic speed shift range. The vehicle speed is preceived as an oil pressure signal proportional to the vehicle speed generated by a governor, while the throttle opening is perceived as another oil pressure signal proportional to the throttle opening generated by a throttle valve. These two oil pressure signals are introduced into one or more shift valves to effect shifting of them thereby selectively engaging or disengaging clutches and/or brakes incorporated in the speed change gears to establish a required speed shift range. Such a shifting of the automatic fluid transmission is generally performed along speed shift lines which coordinate the throttle opening and the vehicle speed. These speed shift lines are characteristic in that a shifting between two speed ranges is effected at a higher vehicle speed when the throttle opening is larger. Furthermore, in order to stablize the operation of the automatic transmission within the shifting ranges, it is adapted to have a hystersis effect in shifting performance so that at the same throttle opening, the downshift is effected at a lower vehicle speed than the upshift.